DC Motor Quiz

A 100V dc machine has an armature resistance of 0.8Ω. If the full load armature current is 15A, fine the induced emf when the machine acts as Generator

A 440V dc shunt motor runs at 1000rpm when the armature current is 45A. calculate the speed if the torque is doubled. Given that Ra =0.5Ω.

A 380V, shunt motor has an armature resistance of 0.5Ω dc machine has an field resistance of 150Ω. Determine the back emf when giving an output of 10 horse power at 80% efficiency.

A d.c. motor operates from a 240 V supply. The armature resistance is 0.2Ω. Determine the back e.m.f. when the armature current is 50A.

The armature of a d.c. machine has a resistance of and is connected to a 300 V supply. Calculate the e.m.f. generated when it is running: (a) as a generator giving 100 A, and (b) as a motor taking 80 A.

A 320 V shunt motor takes a total current of 80 A and runs at 1000 rev/min. If the iron, friction and windage losses amount to 1.5 kW, the shunt field resistance is 40 Ω and the armature resistance is 0.2 Ω, determine the overall efficiency of the motor.

A 250 V series motor draws a current of 40 A. The armature resistance is 0.15 Ω and the field resistance is 0.05 Ω. Determine the maximum efficiency of the motor.

A 200 V d.c. motor develops a shaft torque of 15 Nm at 1200 rev/min. If the efficiency is 80%, determine the current supplied to the motor.

A d.c. series motor drives a load at 30 rev/s and takes a current of 10 A when the supply voltage is 400 V. If the total resistance of the motor is 2 Ω and the iron, friction and windage losses amount to 300 W, determine the efficiency of the motor.